This achievement has you collecting cute little green quilen puppies from around the instance. Once clicked, they will follow you around inside the instance. You can do this achievement as you clear, or go back after you've already beaten the instance. All the dogs are easily found, but require a few extra trash kills.

The first one is straight across from the entrance, off the left side of the little cubby hole.

The second one is in the first boss' room, off to the right side kinda by Haiyan the Unstoppable. It will be hard to see under the boss effects and all the dudes with him. Best to get after the fight has been beaten.

On the third one, you will find him up on a shelf on your right side as you wind down towards the Gekkan. You will need to jump on top of the brazier below him and click the dog as you jump to the side.

The fourth one will be in one of the unlocked vaults, coming down the right-side ramp.

The fifth one is in a room off to the side on the way to the final boss, Xin the Weaponmaster. The room is off to the left side. Inside will be some trash, and three dog statues. Use the scrying orb after defeating the trash. It will destroy the largest dog statue and the final Quilen will be underneath it.

If the group is not cooperative, you can go back after you finished the instance, as Tziva mentioned. Also, the trash will disappear after you kill the last boss, so you won't need to clear extra trash.